This invention relates to displays and more particularly to displays which allow a switching action at the display itself due to the proximity of an operator thereto.
Electrical circuits intrinsically require a switching mechanism to be utilized to direct and alter the flow of data and power. This switching was generally accomplished by a mechanical switch which physically closed or shorted two leads. Recently, a new form of switching has taken place in which the switch itself does not actually do the shorting. In this process a relay switch is activated when the control means receives data indicating that the operator desires a change in the state of operation. Hence, the control means monitors some physical characteristic which is reflective of the operator's actions. This type of switch is generally referred to as a touch switch.
One form of the touch switch involves mechanical movement achieved by forming a conductive touch pad on one surface of a glass panel, and forming a pair of spaced apart conductors on the opposite surface of the glass panel in registry with the touch pads on the one surface. Electrical contact to the spaced apart conductors on the opposite surface of the glass panel requires the use of a complex arrangement of spring contact members affixed to the circuit board or the like. The circuit board is mounted so it is held in registry with a glass panel and the spring contact members make electrical contact with the corresponding ones on the conductor on the opposite surface of the glass panel. When the operator touches and presses on the glass panel it deforms and allows the pads to contact. The control means monitoring this shorting between the pads will utilize this to effectuate a change from state-to-state.
This arrangement though, is complex, relatively expensive to manufacture, and generally requires the assembly to be extremely thick. This thickness may be great enough to accommodate the glass panel, spring contact memory and circuit board on which the spring contact members are mounted. Additionally, this type of switch must be mounted near or in natural association to be independent display or permanent label so that the operator will readily recognize the function which the switch serves.
Another form of the touch switch is referred to as capacitive touch switch. In this form of the touch switch, a touch electrode is placed in such a position that an operator may come in physical contact to allow the natural human capacitance of approximately 100 pico farads (pf) to be communicated to the touch electrode. A pair of secondary electrodes are placed in capacitive communication to the touch electrode. A monitored source signal is communicated to the first of the secondary electrodes which is then capacitively communicated to the last secondary electrode via the touch electrode. By monitoring the capacitance sensed in the last secondary electrode, a control means determines when an operator has touched the primary electrode. The capacitance in the secondary electrode will be altered by the natural human capacitance of approximately 100 pf communicated to the touch electrode by the operator's touch.
Again though, this switch must be matched to a label to communicate to the operator the purpose for which it serves. Additionally, the operator must touch the panel; and, if poor conduction occurs between the operator and the touch electrode, the control means will have difficulty determining if the operator has touched or contacted to touch electrode.
The art of labeling a switch has become very extensive. Numerous means have been developed, in which a label may be applied to a switch.
Labels may be permanent in nature, being affixed to or near the switch. Paint, ink or the like is typically used.
An alternative method to labeling permanently is to label via some sort of alterable display. These displays are typically Liquid Crystal Displays (LCD's), Light Emitting Diodes (LED's ), Gas Discharge Displays, or other such means.
Construction of these displays is well known and well documented in the art. Liquid Crystal Displays and their construction is well documented in the U.S. Pat. No. 3,771,855, issued Nov. 13, 1973, to Carmen Burns, incorporated hereinto by reference.
Another method which to utilizes a liquid crystal display as an input device is that of U.S. Pat. No. 4,224,615 issued Sept. 23, 1980, to Penz. In this switch, the operator must contact and depress the front panel of the liquid crystal display. This deformation causes a change in the capacitance which is monitorable.
Typically, in an operator interface, a switch and a display are matched to each other so that the display communicates to the operator a label for the switch. Note though, that two sets of circuitry are required in this arrangement, one for the display and one for the switch. The display and the switch remain separate units. Another hinderance to this arrangement of switch and display, which form an interface, is that the operator must come in physical contact with the switch. The switch is typically separated in space from the display. Hence, the operator must determine which switch is associated with which of the display.